ESR >70 mm/hr had a sensitivity of 83% and specificity of 77% (positive likelihood ratio [LR+]=3.6; negative likelihood ratio [LR−]=0.22). Ulcer size >2 cm2 had a sensitivity of 88% and specificity of 77% (LR+=3.8; LR−=0.16). Combined, an ESR >70 mm/hr and ulcer size >2cm2 had a slightly better specificity than either finding alone, 82%, but a lower sensitivity of 79% (LR+=4.4; LR−= 0.26).
Serum markers accurately distinguish osteomyelitis from infection
An individual prospective cohort trial of 61 adult patients with diabetes and a foot infection, published after the meta-analysis4 described previously, examined the accuracy of serum markers (ESR, CRP, procalcitonin) for diagnosing osteomyelitis.6 A positive PTB test and imaging study (plain film, MRI, or nuclear scintigraphy) were used as the diagnostic gold standard.
Thirty-four patients had a soft tissue infection and 27 had osteomyelitis. All markers were higher in patients with osteomyelitis than in patients with a soft tissue infection (ESR=76 mm/hr vs 66 mm/hr; P<.001; CRP=25 mg/L vs 8.7 mg/L; P<.001; procalcitonin=2.4 ng/mL vs 0.71 ng/mL; P<.001). The sensitivity and specificity for each marker at its optimum points were: ESR >67 mm/hr (sensitivity 84%; specificity 75%; LR+=3.4; LR−=0.21); CRP >14 mg/L (sensitivity 85%; specificity 83%; LR+=5; LR−=0.18); and procalcitonin >0.3 ng/mL (sensitivity 81%; specificity 71%; LR+=2.8; LR−=0.27).
RECOMMENDATIONS
The Infectious Diseases Society of America (IDSA) recommends performing the PTB test on any diabetic foot infection with an open wound (level of evidence: strong moderate).7 It also recommends performing plain radiography on all patients presenting with a new infection to evaluate for bony abnormalities, soft tissue gas, and foreign bodies (level of evidence: strong moderate).
The IDSA, the American College of Radiology diagnostic imaging expert panel, and the National Institute for Health and Clinical Excellence recommend using MRI in most clinical scenarios when osteomyelitis is suspected (level of evidence: strong moderate).8,9